In the treatment of acute myocardial infarction (MI) reperfusion therapy significantly improves survival. However, an open epicardial coronary artery is not necessarily equivalent to optimal myocardial reperfusion. Despite a widely patent artery, complete reperfusion at the myocardial level may not occur because of occlusion of the microvasulature. The applicant has used contrast-enhanced magnetic resonance imaging (MRI) to document microvascular obstruction or "no-reflow" in patients with reperfused acute MI and correlated it with adverse clinical outcomes. This proposal extends her prior work by applying MRI to the setting of elective percutaneous coronary interventions (PCI), an area in which microvascular obstruction has not been fully described. Specific aims include: (1) Determining the prevalence of microvascular obstruction by MRI after elective PCI; (2) Determining clinical risk factors for development and angiographic and cardiac enzyme correlates of microvascular obstruction; (3) Determining the time course of evolving microvascular obstruction by serial MRI from 2-4 hours to 24 hours to 6 months after PCI; (4) Correlating the presence and extent of microvascular obstruction with global and regional left ventricular function; and (5) Relating the presence and extent of microvascular obstruction to 3-5 year clinical outcome. This study will be performed at the Johns Hopkins Hospital, under the mentorship of Dr. Joao Lima, a leading expert in cardiovascular MRI. Johns Hopkins has extensive MRI facilities and a comprehensive research program that includes extensive collaboration between Cardiology and Radiology. In addition, the School of Public Health is world-renowned. Hence, Johns Hopkins provides the ideal environment for the applicant to achieve her goals of designing and performing clinical trials addressing the pathophysiology of coronary syndromes, using MRI as a tool to answer research questions in coronary syndromes, and expanding the clinical applicability of cardiac MRI.